Grayscale redistribution system to improve retinal imaging by reducing the effect of a highly reflective optic nerve

ABSTRACT

A system is provided to improve retinal camera picture quality by providing a user-variable transfer function for each pixel that results in redistributing grayscale values to solve the problem of saturation caused by highly reflective retinal objects. The result is the ability to capture both optic nerve and retina detail in a single picture. The darker retina is brightened to permit observing retinal detail using the redistributed grayscale values, while preserving optic nerve detail. Those pixels experiencing high-intensity reflections are properly exposed to prevent saturation, while outputs of low-intensity pixels associated with the darker regions are intensified, in one embodiment in accordance with an adjustable Bezier curve. The result is that one can obtain retinal details previously flooded out by the reflections from the optic nerve while at the same time offering optic nerve detail. In one embodiment the redistributed grayscale values are optimized for each color plane to provide color-corrected images matching those associated with film cameras.

FIELD OF THE INVENTION

This invention relates to retinal cameras and more particularly to asystem for eliminating the effects of a highly reflective optic nerve sothat detail of both the optic nerve and detail of the surroundingretinal material are viewable.

BACKGROUND OF THE INVENTION

In retinal imaging, one seeks to obtain photographs of the detail of theoptic nerve and the surrounding retinal material that heretofore hasbeen captured on film.

A constant problem in retinal imaging is the fact that the optic nerve,which is basically where all of the nerve bundles go back to the brain,is very reflective. When one fires a strobe into the eye to illuminatethe retina, the optic nerve tends to throw large amounts of light backat the camera, which shows up as a bright blotch at the position wherethe optic nerve is attached to the retina. The rest of the detail of theretina that one wants to see, especially at the periphery, is very dark.The result of photographing the retina utilizing high-power strobe pulseillumination is a very high-contrast image where the darker regions aredrowned out by the high reflectivity of the optic nerve.

More importantly, the optic nerves of the darker-skinned races,including the Negroid and Hispanic races, are in general more highlyreflective than white or Caucasian races, making retinal imaging evenmore difficult. It is noted that people of darker complexion have darkerretinas because the pigment of the retina is darker.

When taking retinal images, one has to inject enough light to illuminatethe dark areas. However, if one increases the output of the xenon strobenormally used, one simply drowns out the optic nerve detail because ofits high reflectivity.

In the past, in order to obtain images of the detail of the optic nerveas well as images of the retina, one had to take numbers of photographs,each with different light outputs or different F stops on the camera.With multiple pictures one needs multiple strobe pulses, with eachstrobe pulse injecting energy into the eye. This causes pain and is veryuncomfortable for the patient. What this means is that a patient mayhave to endure a number of 100 watt-second pulses discharged into theeye. It is therefore desirable to be able to eliminate the requirementfor multiple exposures.

However, the problem is not so much seeing the remainder of the opticnerve but dealing with the high reflections where the optic nerve isattached to the retina that visually resembles a hole in the back of theeye. As will be appreciated, the optic nerve is always on the nasal sideof the eye and appears as an offset bright hole. On the other hand, theretina has blood vessels and arteries that stretch out across the eyeincluding smaller capillaries that branch off. In general, the vascularstructure forms a circular pattern. At the center of vision, which iscalled the macula, there are no blood vessels and therefore it iscompletely devoid of blood vessel structure.

It is noted that in addition to the optic nerve, pathology can be highlyreflective as well. High reflections can come from a scar, tumor orgrowth, the reflections from which will saturate the camera with theintroduction of a pulse from the xenon strobe.

As mentioned hereinabove, one technique to eliminate the problems ofbeing able to view the structure of the eye is to have multiplephotographs, one to expose the optic nerve and the other to expose therest of the retina. In order to get the detail of the optic nerve, onecould either reduce the output of the flash lamp or stop down the cameraso that just this area is properly exposed to be able to see all thedetail. However, by cutting down the flash power to be able to observethe optic nerve detail, one has insufficient light to be able to viewthe remainder of the retina. Note that with too high a strobe output thestrobe saturates the camera due to the reflectivity of the optic nerveand all detail is gone.

As will be apparent, by raising the flash lamp power output one wouldsimply see hotspots in the image for which detail is completely lacking.

In the past, in order to be able to view the detail of the retina awayfrom the optic nerve, the typical practice was to slightly increase theflash lamp output which, while causing hotspots near the optic nerve orthe pathology, it was possible to discern the detail of the darkenedportion of the retina.

There is therefore a necessity for eliminating the requirement formultiple photographs, both from a patient comfort point of view and tobe able to view all of the retina in a single image or photograph.

With the advent of digital cameras, usually having CCD sensor arrays ofa 1- to 11-megapixel variety, it is possible to get real-time images ofthe retina. However, the problem of multiple pictures and flash lampintensity versus optic nerve reflectivity has not as yet been resolvedfor the above reasons.

SUMMARY OF INVENTION

Rather than taking multiple exposures to obtain retinal and optic nervedetail, in the subject invention one exposure is used and a single imagecarries both optic nerve and dark retina detail. To make this possible,flash lamp intensity is lowered to avoid saturation and for obtainingoptic nerve detail; and pixels viewing the low-intensity, now furtherdarkened retinal regions have their outputs amplified so that the darkregions are brightened to reveal the detail. Note that the ability tosee all aspects of the eye in one image or photograph aids diagnosis.

How this is accomplished is now described.

It will be appreciated that the pixels in a digital camera have outputsthat are ascertainable. The dynamic range of each output ischaracterized by a grayscale having a range from 0 to 255, such that onecan obtain 256 shades of any one color or gray. The grayscale in essencedefines the dynamic range of the camera and to a certain extent thecolors of the observed image.

In general, the outputs of each of the pixels of the array can becharacterized by a transfer function that is linear, meaning a linearrelationship between the input and the output. Normally thisrelationship of input to output is fixed and is dependent upon thecharacteristics of the digital camera.

Since each of the outputs of the CCD array of the digital camera isaddressable, one can arrange to weight the individual outputs ofindividual pixels of the CCD array so as to increase the transferfunction between input and output for those input levels or intensitiesthat are relatively low.

Thus as one part of the subject invention, those pixels from the darkretina having a relatively low intensity have their outputs amplified tobrighten those areas so that detail is visible. As a result, one canascertain which of the pixels have relatively low outputs and multiplytheir inputs with a weight determined from a lookup table that willincrease the output while not affecting the transfer functions for thepixels having higher outputs.

By increasing the outputs of the pixels having low-intensity inputs, onecan obtain detail of the dark retinal area.

To obtain detail of the optic nerve and other highly reflective retinalobjects, one first reduces flash lamp output to prevent saturationcaused by reflections from the optic nerve or other highly reflectiveobjects. Once having reduced the flash lamp output to avoid saturationone can view detail of the highly reflective retinal objects such as theoptic nerve. However, reducing the flash lamp output further darkens theretina. With the subject technique the further darkened portions of theretina are brightened by the increased outputs for the low-outputpixels. Thus both the optic nerve detail and the detail of the remainderof the retina are simultaneously viewable with one exposure in onepicture. This solves the problems associated with multiple exposures.

The weighting function used, rather than being a linear weightingfunction, is alterable in one embodiment by utilizing a Bezier curve,the curvature of which is determined by four points, with two pointsbeing fixed and two points being variable. Given a Bezier curve todefine the grayscale distribution, if one lowers the curve at the centerportion to provide a belly, generally in the 220 to 240 grayscale range,then pixel outputs that are the result of the darker regions areincreased.

In one embodiment the weighting system is user variable so that the usercan move the belly of the curve up and down under the operator'scontrol. This means that the operator can control the transfer functionfor all of the pixels, most notably the ones in the mid grayscale rangescorresponding to dark areas, simply by moving the variable points of theBezier curve.

Thus what is done in the subject invention is to redistribute thegrayscale values in a non-linear fashion along a curve so that the darkareas get bright while at the same time not significantly amplifying theoutputs of those pixels that are detecting the high-reflectance opticnerve. The result is to be able to view the detail of the highlyreflective materials in the eye while at the same time viewing thedetail of the dark retina, and to do so with one exposure taking onepicture.

The optimal nonlinear grayscale distribution takes the darker areas andmakes the subtle details more exaggerated, while at the same time mutingthe changes in the lighter areas to produce a flattening effect.

Note that for the high-intensity pixels the transfer function mutes theamplification, thereby to mute the output. In short, for brighter lightareas one is not transferring as much gain to the output for theparticular pixel, whereas for the dark areas one is providing gain, withthe weights specified by a look up table.

In one operating scenario, the first thing that one wants to do is toreduce the power of the flash lamp. The reason that one wants to reducethe power of the flash lamp is to limit the amount of reflection fromthe optic nerve. Thus one wants to get away from the situation where thereflection from the optic nerve saturates everything.

Then one adjusts the grayscale distribution to correct for the effect ofthe lowered flash lamp intensity on the darker regions of the retina byamplifying the output for low-intensity pixels, while at the same timeleaving the transfer functions for the bright area pixels alone so thatthe transfer function for these pixels remains the same.

In summary, one cuts down the output of the flash lamp to eliminategross saturation and then increases brightness of the dark regions orthe low-intensity areas while at the same time keeping the others at thesame level. This pops out the detail in both the darker regions and thebright regions.

It is possible to decrease the amplification for those pixels viewingdarker regions to make the darker regions darker; but in so doing onewould have a very high contrast effect, which is undesirable. The ideain color retinal imaging is not to create contrast but to balance it.Contrast is basically taking the dark regions and making them darker andtaking the light regions and making them lighter.

In order to obtain a realistic view of the retina in terms of an image,one is trying to do just the opposite, namely trying to take everythingand flatten the response out so that the image looks natural. This aidsin the interpretation of the pathology of the retina so that what anophthalmologist is looking at corresponds as nearly as possible to thatwhich exists in nature. One in short does not want to create artificialconditions or artifacts that could in some sense make a diagnosis moredifficult.

There is, however, another aspect to the use of the non-uniformgrayscale distribution and that is to make the image available from thedigital camera correspond to the images available from film. The reasonthat this is important is because many doctors are used to viewing filmimages in order to make diagnosis and would like to have the images thatare available from the digital camera more closely correspond to whatthey are used to looking at.

By using the Bezier curve, which provides a polynomial fit between fourpoints, and by adjusting the transfer function of each of the pixelsbased on the curve, one can adjust the curve to not only fix the problemof hotspots versus dark areas of a retina but also to correct the colorresponse of the digital camera.

For each retinal camera, a model is generated to create what are calledcolor planes or curves. These curves in essence describe the transferfunction for each of the pixels in the camera. Since the colordistribution curve is the composite of the red, green and blue responseof the camera, by adjusting these curves one can make adjustments foreach color. This is done by generating red, green and blue curves,altering them and then forming a color composite curve.

This is important to help compensate for flash temperatures. In generalthe output of a xenon flash strobe looks a little blue. One can correctto a realistic view by compensating for the blue illumination throughadjusting the red and green response of the digital camera.

It is noted that film images tend to be very yellow when the images areobtained by illuminating the retina with a blue-shifted xenon output.This is because film in general is somewhat blue-muted. Thus when onetakes photographs of the retina on film, they tend to have a slightyellow-orange look to them that might not necessarily be real but thatwhich doctors are generally used to seeing.

In order to adjust the output of the CCD digital camera to provideyellow-orange, one wishes to make the output of these cameras look likewhat would be seen when using a film camera. One therefore actuallyseeks to mute the blue channel for the digital camera and can do so bygenerating weights from a nonlinear grayscale distribution.

Thus by using the Bezier curve and plugging in the red, green and bluecharacteristics of each color, one can make the images from the digitalcamera approximate that which would be seen utilizing a film camera andyet still be able to pop out the dark areas of the retina and the detailof the highly reflective retinal objects.

In summary, a system is provided to improve retinal camera picturequality by providing a user-variable transfer function for each pixelthat results in redistributing grayscale values to solve the problem ofsaturation caused by highly reflective retinal objects. The result isthe ability to capture both optic nerve and retina detail in a singlepicture. The darker retina is brightened using the redistributedgrayscale values to permit observing retinal detail, while preservingoptic nerve detail. The optic nerve and other highly reflective retinalobjects are properly exposed by reducing flash lamp output to preventsaturation, while outputs of low-intensity pixels associated with thedarker regions are intensified, in one embodiment in accordance with anadjustable Bezier curve. The result is that one can obtain retinaldetails previously flooded out by the reflections from the optic nervewhile at the same time offering optic nerve detail. In one embodimentthe redistributed grayscale values are optimized for each color plane toprovide color-corrected images matching those associated with filmcameras.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the subject invention will be betterunderstood in connection with a Detailed Description, in conjunctionwith the Drawings, of which:

FIG. 1 is a diagrammatic illustration of a retinal camera, including afilm camera, a digital camera, and drive for driving a strobe lamp so asto illuminate the retina of an eye;

FIG. 2 is a diagrammatic illustration of a computer system used toweight the outputs of the CCD array in the digital camera of FIG. 1 soas to be able to output a single digital image containing detail of theretina and the optic nerve;

FIG. 3 is a series of images created by the digital camera of FIG. 1,illustrating an image of the retina showing a darkened image the resultof reducing flash lamp output to eliminate saturation; an image usingnormal flash lamp outputs illustrating the saturation due to thereflections from the highly reflective optic nerve and other pathology;and am image showing the result of applying a nonlinear grayscalefunction to produce a compensated image in which retinal and optic nervedetail are obtained in one exposure;

FIG. 4 is a series of graphs illustrating the control of the weightsused in generating the images of FIG. 3, showing linear distribution forthe dark and normal images and a Bezier curve defining the weights forthe compensated image of FIG. 3;

FIG. 5 is a diagrammatic illustration of the specification of weights ina look up table through manipulation of a Bezier curve, with thespecification of the weights dependent upon the pixel output level;

FIG. 6 is a graph showing that for a dimly illuminated pixel, moving theBezier curve of FIG. 5 downwardly results in a 28% increase in theoutput, thus generating a weight of 1.28 by which the output of theassociated pixel is multiplied;

FIG. 7 is a graph of the Bezier curve of FIGS. 4, 5 and 6, illustratingthat the Bezier curve defines pixel output level based on input level,with the Bezier curve defining the transfer function for the particularpixel;

FIG. 8 is a flow chart showing the operation of the subject system fromimage capture through the production of a corrected image;

FIG. 9 is a diagrammatic illustration of the use of a non-lineargrayscale distribution function to color-compensate a digital camera;and, FIG. 10 is a graph showing the Bezier curves for blue, green andred compensation and the resultant composite Bezier curve.

DETAILED DESCRIPTION

Referring now to FIG. 1, prior to discussing the subject retinal imageoptimization system, the operation of a typical retinal camera isdiscussed. Here a retinal imaging camera 10 includes a film camera 12and a digital camera 14 mounted on a stand 16 such that an imagingsystem 18 images the retina 20 of eye 22 onto the focal planes ofcameras 12 and 14. In order to illuminate retina 20, a xenon strobe lamp24 has its output redirected by mirrors 26 and 28 out through imagingsystem 18 so that the output of xenon strobe 24 illuminates retina 20.Note that an eyepiece 30 is used for focusing both the digital and filmcamera as well as directing the optics to the appropriate portion of theeye.

A precise maximum strobe output includes the use of drive 32 thatincorporates a power supply for delivering several hundred volts to thexenon strobe. As illustrated, this is accomplished by delivery of aseveral hundred-volt pulse 35, with a pulse width of between 5 and 10milliseconds. In one embodiment the strobe is activated by a foot switch34.

It will be appreciated that foot switch 34 is also used to controlcamera 10 over line 36 to take the pictures such that any shuttering andexposure for either the film camera or the digital camera is controlledresponsive to foot switch 34; or is actuated automatically if desired.

As illustrated in FIG. 2, a monitor 46 is used to display the retinalimage as well as to display the aforementioned Bezier curves. Monitor 40is coupled to a computer 42, with mouse 44 being used to specify thevariable points of the Bezier curve. Note a keyboard 46 is used as afurther input device.

Referring now to FIG. 3, activation of the xenon flash lamp of FIG. 1results in an image of the retina along with the optic nerve attached.Note in the bottom photograph the retina is dark due to the lowering ofthe flash lamp output to eliminate saturation. While detail of some ofthe retina and the optic nerve can be seen, in general one must lightenup the dark retinal material in order to observe its features, and do sowithout causing saturation. The middle picture shows the result of usingmaximum flash lamp power. Here it can be seen that there are saturatedareas that are completely whited out, thus destroying detail.

The upper picture shows a compensated image in which not only is thedarker retinal area lightened to make retinal detail visible, the opticnerve detail is also visible.

The upper image is the result of applying a pixel weighting function.The weighting function affects the pixel transfer function byselectively amplifying the outputs of the low-intensity pixels. Here itcan be seen that not only is the detail of the optic nerve observable,so also is the detail of the remainder of the retina, including all ofthe vascularization. It will be appreciated by the decreasing the flashlamp intensity to eliminate saturation coupled with the nonlineargrayscale weighting system that one can observe both the optic nervedetail and the detail of the darker surrounding retinal material in asingle image. This aids diagnosis. An additional advantage is that onlyone photograph or one exposure per image need be made to obtainsufficient detail of all areas of the retina, thus limiting the painassociated with multiple exposures.

Referring to FIG. 4, adjacent each of the dark, normal and compensatedimages is the corresponding curve that defines the weighting system usedto weigh the outputs of the individual pixels. The lower and middlecurves correspond to a linear distribution is used, meaning that foreach pixel in the CCD array, its output is a fixed percentage of theinput. This transfer function is the characteristic of the camera and isnot altered.

However, the top graph shows a Bezier curve that defines the weights tobe applied to the pixels.

Referring now to FIG. 5, how an individual pixel output is weighted isnow described. Here it can be seen that the weights applied to a pixelare derived from a look up table 50 coupled to a computer 52. Look uptable 50 is arranged to output a specified weight to be multiplied bythe output of an addressed pixel, with the weight stored in the look uptable being determined from the Bezier curve calculated by the computer.

The computer generates the Bezier curve on display 54, which for each ofthe 256 grayscale input levels determines an output level. Thus for aCCD array 56, a pixel 58, defined as pixel X_(m)Y_(n), has its outputamplified at 60, after which a weight is applied to its output by aweighting circuit 62.

The output of amplifier 60 is coupled to look up table 50 so that theinitial level of the pixel can be ascertained. The look up tableascertains the grayscale input level for this pixel and ascertains theweight to be applied to the pixel output based on its input level. Thisweight is coupled over line 66 to unit 62 to apply a predeterminedmultiplication factor or weight to the output of amplifier 60.Alternatively, the table originally has values corresponding to a linearcurve. The weighting is accomplished by reassigning the red value withthe new y-intercept point on the curve.

As will be described, mouse 70 controls the curve 72 displayed atdisplay 54 by in effect moving variable points 74 and 76, with points 78and 80 being fixed. The line between the four points is generated usinga Bernstein polynomial fit program such that the weights specified bylook up table 50 can be controlled by user interface 80 comprised ofcomputer 52, mouse 70 and display 54.

In the illustrated embodiment, an input level Ix_(m)y_(n) is illustratedby dotted line 82, whereas the associated output level for such an inputlevel is indicated by dotted line 84.

Referring to FIG. 6, dotted line 82 intercepts Bezier curve 72 at point86, which as illustrated by arrow 88 specifies a 28% increase in outputover that which would have occurred if curve 72 were linear asillustrated at 90. Thus curve 72 specifies for an input illustrated byline 82 that there should be a 28% increase in the output for thisparticular pixel over that associated with a linear grayscale function.

Referring to FIG. 7, the graph shows the intersection with Bezier curve72 of a number of different grayscale input levels illustrated by lines82. In one embodiment, the grayscale is divided up into 256 levels. Foreach grayscale level there is an associated output. As can be seen fromthe low input levels at the mid range of the graph as illustrated at82′, the output at 84′ is amplified over that specified by a linearrelationship between input and output. Thus for the lower input levelsthe output associated with the particular pixel is highly amplified.However, for the higher input levels it will be seen that with the inputlevel just below saturation as shown at 82″, the output level is notsignificantly amplified. At this point the Bezier curve approximates alinear curve. How much the output for a given pixel input level isvaried is therefore determined by the intersection of the input levelwith the Bezier curve.

How this is accomplished is illustrated by the flowchart of FIG. 8 inwhich the image is captured as illustrated at 90. The capture isaccomplished with high-bit definition as illustrated at 92 that involves12 bits or 4,096 levels. This resolution is reduced as illustrated at 94in one embodiment by conversion to an 8-bit system with 256 values. Theresultant 8-bit values are passed through the Bezier curve look up tableat 96 to produce image 98. This image is the corrected image, with thevalues for each pixel being multiplied by a weight determined by thelook up table.

As can be seen, the look up table values can be changed as describedabove and as illustrated at 100, with the new values loaded into look uptable 102.

Referring now to FIG. 9 in which like elements between FIGS. 5 and 9have like reference characters, it is possible to color-correct thedigital camera using the subject system by adjusting the initial red,blue and green Bezier curves for blue color correction. The compositegrayscale curve, being made up of the red, green and blue components,determines the color output of the camera and can be used to correct forthe normal blue shift associated with xenon flash tubes.

In order to provide initial color correction, the weights generated byunit 62 include the color correction weights for each pixel, hereWix_(m)y_(n). This refers to the initial color correction weights.

It will be appreciated that individual weights can be assigned toindividual pixels to provide overall color correction. The compositeBezier curve permits tailoring or tweaking of the individual pixeloutputs so as to provide improved color correction prior to correctingthe overall image for brightness. Here it can be seen that thebrightness correction weights, Wx_(m)y_(n), are added to the colorcorrection weights, Wix_(m)y_(n), so that the weight generated for agiven pixel is both the color corrected output for the pixel and thebrightness correction output for the pixel.

Referring to FIG. 10, it will be appreciated that for a given colorcamera one can generate blue, green and red Bezier curves which, whencombined into a composite Bezier curve, weight the output of the pixelsof the digital camera based on pixel intensity levels.

Put another way, these curves, generally defining so-called colorplanes, define the initial transfer function for each pixel based oninput level. The color plane curves correct the image for the slightlyblue tint of the xenon flash lamp.

The brightness compensation curve is applied after initial compensationto provide for the subject brightness control.

Also shown in this figure is the use of two variable Bezier points togenerate the blue curve. Thus it can be seen that the three curves canbe specified by two fixed points and two variable points, although moreflexible points can be added if desired.

Thus one can weight the outputs of the pixels based on input levels tobe able to select the lower illuminated pixels and to heavily amplifytheir outputs while only slightly amplifying high-intensity pixels. Theresult is a flattening that permits viewing detail not only in the darkretinal areas, but also detail in the highly reflective regions; and todo so with only one exposure in a single image or picture.

A program listing in C follows describing the generation of the Beziercurve, the operation of the look up table and the generation of theweights required to provide the corrected image.

While the present invention has been described in connection with thepreferred embodiments of the various figures, it is to be understoodthat other similar embodiments may be used or modifications or additionsmay be made to the described embodiment for performing the same functionof the present invention without deviating therefrom. Therefore, thepresent invention should not be limited to any single embodiment, butrather construed in breadth and scope in accordance with the recitationof the appended claims.

1. In a digital retinal camera having a sensor including an array ofpixel elements, a method for improving retinal imaging for retinalimages degraded by saturation due to highly reflective retinal objects,comprising the steps of: adjusting the flash lamp output of the retinalcamera to a point at which the detail of highly reflective retinalobjects is observable; and, amplifying the returns from non-highlyreflective retinal objects to brighten them to an extent that the detailof the non-highly reflective retinal objects is observable, whereby bothhighly reflective and non-highly reflective retinal objects areobservable in one image, thereby eliminating the requirement formultiple exposures to obtain retinal image detail.
 2. The method ofclaim 1, wherein the amplification for the non-highly reflective retinalobjects includes the use of a user-variable transfer function thatapplies weights to the outputs of the sensor array elements in theretinal camera that result in a redistributed grayscale.
 3. The methodof claim 2, wherein the user-variable transfer function defines weightstailored for each pixel.
 4. The method of claim 3, wherein theuser-variable transfer function is defined by a variation from a lineartransfer function.
 5. The method of claim 4, wherein the weight for eachpixel is determined by an adjustable Bezier curve having a curvaturespecified by the user.
 6. The method of claim 1, wherein theamplification for each pixel is determined by associated transferfunction weights.
 7. The method of claim 6, wherein the transferfunction weight for each pixel is determined by a look up table.
 8. Themethod of claim 7, wherein the weights stored in the look up tableinclude values determined by the user.
 9. The method of claim 8, whereinone input to the look up table includes the intensity level of a pixeland wherein the look up table outputs the weight associated with theinput intensity level of the associated pixel.
 10. The method of claim9, wherein the weight outputted by the look up table is that associatedwith a user-defined Bezier curve.
 11. The method of claim 1, and furtherincluding the step of color-correcting images from the digital camera byinitially specifying transfer function weights for each pixel level interms of a grayscale distribution to color shift the images associatedwith the digital camera to match those expected from film cameras. 12.The method of claim 1, wherein specifying the transfer function for eachpixel results in redistributing the associated grayscale values.
 13. Agrayscale redistribution system for improving retinal imaging from adigital camera including an array of sensor elements, each defining apixel, to permit capture of the digital image in one exposure so as toreveal detail of both highly reflective retinal objects and non-highlyreflective retinal objects in one image, comprising: a system forweighting the outputs of individual pixels in accordance with the outputlevel of a pixel so as to amplify the output of those pixels viewingdarker retinal regions.
 14. The system of claim 13, and furtherincluding a look up table for specifying the weights provided by saidweighting system.
 15. The system of claim 14, wherein the weightspecified by said look up table is defined by the intersection of thepixel output level with a curve, whereby the output of a predeterminedpixel is weighted by said intersection.
 16. The system of claim 15,wherein said curve includes a Bezier curve.
 17. The system of claim 16,wherein said Bezier curve is determined by two fixed points and liesbelow a straight line between said two fixed points, said straight linedefining a linear curve.
 18. The system of claim 17, wherein said Beziercurve is user controllable.
 19. The system of claim 18, wherein theweights specified by said look up table include an amplificationcomponent and a color correction component, said color correctioncomponent being derived from the composite of color plane curves, saidcolor plane curves being altered to correct the retinal image from saiddigital camera to more closely correspond to the retinal image one wouldexpect from a film camera.
 20. A method for providing a retinal imagefrom a digital retinal camera employing a flash lamp so as to makeviewable detail of both highly reflective retinal objects and non-highlyreflective retinal objects in a single exposure, comprising the stepsof: reducing the flash lamp output to a point at which detail of highlyreflective retinal objects is viewable in the image produced by thedigital camera; and, redistributing the camera grayscale to amplifypixel outputs associated with non-highly reflective retinal objects to apoint where they are viewable, whereby an image having sufficient detailin all retinal areas can be made of the retina in one exposure, thus toeliminate multiple exposures of the eye while at the same time renderingretinal detail of both highly reflective and non-highly reflectiveretinal objects in a single image for improved diagnostic purposes. 21.The method of claim 20, wherein the clarification of the non-highlyreflective retinal objects to permit viewing the detail thereof whichhas been darkened due to the reduction of the flash lamp output is usercontrollable.
 22. The method of claim 20, wherein the redistributedgrayscale includes a redistribution that also color corrects the retinalimage so that it more closely approximates an image that would beavailable from a film camera.
 23. A method for minimizing exposure of apatient to high-intensity strobe flashes of a retinal camera when takingpictures of the retina, comprising the step of: generating a retinalimage in a single exposure that presents detail of both highlyreflective retinal objects and non-highly reflective retinal objects ina single picture.
 24. The method of claim 23, wherein the step ofrendering a single image having retinal detail includes redistributingthe grayscale associated with the retinal camera so as to amplify theoutputs of pixels in the retinal camera viewing dark areas of the retinamore than those pixels viewing highly reflective retinal objects.